Pulsed laser systems, such as excimer lasers, are well known. FIG. 1 is a side view of a laser chamber 10 used in a pulsed laser system. Laser chamber 10 includes an electrode structure 12, a blower 14, windows 16, 18, a laser beam 20. Between electrode structure 12 is the laser discharge region 24.
FIG. 2 is a front view of laser chamber 10. As shown in FIG. 2, laser chamber 10 additionally includes heat exchanger 26, a pre-ionizer 28, baffles 30 and a current return 32, which is used to connect the lower of electrodes 12 to ground.
As well known by those skilled in the art, a pulsed laser system, such as an excimer laser, produces high energy, high frequency pulses in a gas that is between electrodes 12 in laser chamber 10. The gas, which may contain krypton and fluorine, is maintained at high pressure, for example 3 atm. Pre-ionizer 28 first floods the gas within discharge area 24 with free electrons (10.sup.6 to 10.sup.7 per cm.sup.3). Once the gas within discharge area 24 is conditioned with a sufficiently increased electron density, electrodes 12 produce a high energy discharge, which may be for example 15-50 kV. The lasing action from the high energy discharge occurs within 100 nsec from the time of discharge.
The high energy discharge in discharge area 24 produces a large amount of local heating and pressure disturbances in the gas. The thermal and pressure disturbances change the index of refraction of the gas, which has a deleterious effect on the energy efficiency of the laser system. The high energy discharge of the gas does not affect the lasing action from the pulse that caused it because the lasing action occurs within a short amount of time after the high energy discharge, approximately 100 nsec. However, subsequent high energy discharges, which occur at a frequency of approximately 1 KHz, will be produced in the highly disturbed, thermally energetic gas unless the gas is circulated within laser chamber 10. Thus, blower 14 is used to circulate the gas within laser chamber 10. Heat exchanger 26 is placed in the path of the gas flow to cool the gas as it circulates. Typically, the gas in laser chamber 10 is circulated at a speed of 20-30 meters per second through discharge region 24, however, this speed is dictated by the frequency of the pulsed laser system.
It is desirable for the circulating gas within laser chamber 10 to be as uniform and as stable as possible, i.e., thermally, optically, and kinetically stable, because a stable gas maximizes the energy output of the laser system. One cause of disturbance in the gas is shock waves generated from the high energy discharge from electrodes 12. Shock waves from the high energy discharge are reflected by the walls of laser chamber 10, as well as from heat exchanger 26 and other components, back into discharge area 24 where the shock waves interfere with the energy output of the pulsed laser system.
Another cause of disturbance in the gas that is circulating within laser chamber 10 is heat exchanger 26. Although heat exchanger 26 is necessary to cool the thermally excited gas, heat exchanger 26 acts as a choke to the gas flow within laser chamber 10. Consequently, blower 14 is required to overcome the impedance of heat exchanger 26. Further, the position and configuration of heat exchanger 26 disturbs the uniformity of the circulating gas. Fins (not shown) on heat exchanger 26 are conventionally used to assist in heat exchange. However, fins, which are typically one inch high and 0.1 inch apart, further impede the flow of the circulating gas.
In addition, laser chamber 10 fails to circulate the entire volume of gas. The flow of the gas in laser chamber 10 is illustrated by arrows, as shown in FIG. 2. Baffles 30 are used in conjunction with blower 14 to guide the gas flow around laser chamber 10, nevertheless, there are typically dead areas within laser chamber 10 where the gas fails to circulate properly. For instance, laser chamber 10, as shown in FIG. 2, has a dead area in the center of laser chamber 10 where the gas circulates in a small area, i.e., an eddy, and thus fails to circulate throughout laser chamber 10.